The present disclosure relates to an image reading device that is used in digital copiers, image scanners, and the like to scan and read a document, to an image forming apparatus provided with one, and to an image reading method.
Some conventional image reading devices incorporated in multifunction peripherals and the like using an electrophotographic process include a document conveying device (automatic document feeder) that sends a document in sheet form to a document stage (contact glass) to read it, and discharges it from the document stage after reading it. Such an image reading device allows two kinds of reading methods, namely, a sheet-through method in which, while a reading module is fixed at an image reading position, the document conveying device automatically conveys and reads a document, and a fixed-document method in which, while the document on the document stage is replaced one by one with a document presser opened and closed every time a document is read, the reading module is moved to scan and read the document placed on the document stage.
In the image reading devices described above, density difference may arise between the image data read by the fixed-document method and that read by the sheet-through method. For example, when image data is read by the fixed-document method, a document is pressed by a cover member against the contact glass to make close contact with the contact glass. On the other hand, when image data is read by the sheet-through method, a document may be conveyed while being away from the contact glass at the image reading position.
In that case, the distance between a document and the contact glass when image data is read by the fixed-document method is different from that when image data is read by the sheet-through method. Thus, the density of the image data read from a document by the sheet-through method is higher (darker) than that of the image data read from a document by the fixed-document method.
To cope with that, in one known image reading device, by performing shading correction using an adjustment value previously acquired for each of a plurality of reading methods, the difference in the image density in image data caused by the difference in the reading method can be reduced. Specifically, based on image data read from a prescribed reference density document by each reading method, adjustment values for the different reading methods are acquired respectively.